* Monsoon covers India about a month ahead of schedule
* Swiftest-ever monsoon coverage for India -Met official
* To boost early sowing in summer crops (Adds impact over drought areas, short-term forecast)
By Rajendra Jadhav and Ratnajyoti Dutta
MUMBAI/NEW DELHI, June 17 (Reuters) - India's monsoon rains have covered the entire country a month ahead of schedule, brightening the prospects for a bumper output of summer-sown crops such as rice, oilseeds and cotton in one of the world's leading producers.
The rains usually cover all of India by mid-July, but this year it happened on June 16, the earliest such occurrence on record, a senior official at the India Meteorological Department said.
A strong start to the monsoon aids farm output as about 55 percent of the south Asian nation's arable land is rain-fed. It can also help hold down inflation, a critical concern for India's coalition government, which is preparing for national elections in 2014.
The farm sector accounts for about 15 percent of India's near $2-trillion economy, Asia's third-biggest.
"We expected an early coverage, but not so fast," said the Meteorological Department official, who did not want to be named as he was not authorised to speak to the media.
"A very strong pulse over the northwest region helped the monsoon to cover the entire country last night," said another weather official.
Analysts said the early rains should help boost output of summer crops by giving them more time to mature.
"An early sowing of summer crops like rice, cane, soybean, corn and cotton will give them more time to mature and lead to higher yields," said Prasoon Mathur, senior analyst at Delhi-based brokerage Religare Commodities.
Heavy showers would also help soften soils in drought-hit areas, including the major cane-growing state of western Maharashtra, Mathur added.
Maharashtra was hit by drought last year and needs plentiful and timely rain to assist a recovery.
Farmers expect to see power costs fall as early monsoons reduce the need for irrigation, said Sudhir Panwar, president of farmers' group Kishan Jagriti Manch.
The current strong phase in the four-month long rainy season is expected to last through this week, and could then slow early next week, the first official said.
But overall rainfall during the first month of the monsoon is seen as remaining above average.
Last week, the weather office retained its forecast for an average monsoon for this year, riding on a timely start to the season on June 1. (Editing by Himani Sarkar)